1. Field of the Invention
The present invention pertains to a process for producing spherical oxide particles with a low wear rate, which are particularly suitable as catalyst carriers. The present invention also pertains to the production of catalysts from these particles.
2. Prior Art
Spherical oxide particles are used in many applications, including, for example, adsorption, and many catalytic applications. They can be applied in fixed bed, moving bed, or ebullated bed applications. In the present specification, the present invention and its advantages will be described with reference to catalysts suitable for hydroprocessing of hydrocarbon feeds. Nevertheless, as the skilled person will recognize, many of the advantages of the process according to the invention will also be important in other applications.
One of the steps in the preparation of ready-for-use products from heavy hydrocarbon oil fractions is hydroprocessing to effect the complete or partial removal of impurities. Heavy feedstocks, such as feeds based on atmospheric residual oils, vacuum residual oils, tar sand oils, and shale oils generally contain organic sulfur compounds and metallic components. These impurities can be removed by contacting the feedstock with a hydroprocessing catalyst at elevated temperature and pressure in the presence of hydrogen. This will cause the organic sulfur compound to be converted to H2S, while the metals precipitate on the catalyst particles.
The use of non-fixed bed processes, such as moving bed processes and ebullated bed processes, is becoming increasingly important in the hydroprocessing of heavy hydrocarbon feedstocks. Non-fixed bed processes have the advantage that it is not necessary to replace the complete catalyst inventory at the same time. Additionally, the contamination of the catalyst inventory with contaminant metals will be more homogeneous. However, the use of a catalyst in a non-fixed bed application places additional requirements on the properties of the catalyst. In particular, the strength and the abrasion resistance of the catalyst become more critical, because the catalyst particles suffer more wear and tear by colliding with each other and with the walls of the unit. In consequence, the conventional extrusion-shaped catalyst particles are less suitable for use in non-fixed bed processes, because these particles have corners which may easily wear down in these applications. Further, because the catalyst is continuously or intermittently fed to or removed from the reactor, it must have such a form as to allow easy flowing and transfer as a slurry containing the reacting substances.
Therefore, for use in non-fixed bed applications spherical catalyst particles are desirable. Additionally, spherical catalyst particles can also be desirable for use in fixed-bed applications, particularly at the front of a catalyst bed to catch particulate materials, such as solid iron and carbon particles present in the feed. The size of the spherical particles depends on the application, but particles of 0.5 to 7 mm diameter, preferably about 2 mm to 5 mm in diameter are being commonly used at present.
Various processes for preparing spherical oxide particles have been described in the art.
EP 0 025 900 describes a process in which a shapeable dough is extruded and divided into particles, after which the particles are formed into spheres, which are then dried and optionally calcined. The extrusion is preferably through circular holes. The forming into spherical particles can, e.g., be carried out using a rotating plate.
GB 1 535 807 describes a method for preparing spherical alumina particles in which a shapeable dough is extruded, after which the extrudate is segmented and balled, and the balls are dried and calcined.
Japanese Patent Laid-Open No.1973-51882 describes a method of forming particles by vertically and horizontally vibrating shaped particles. Moreover, Japanese Patent Laid-Open No.1974-98378 describes a method of feeding a raw powder or shaped particles into a tilted rotary granulator, for granulation. Japanese Patent Publication Nos. 1984-2649, 1984-21651, and 1985-25182 disclose methods of introducing a raw powder into a horizontal turntable while adding a binder solution for granulation.
However, the particles obtained by the granulation methods in which a powder is used as starting material have a dense, hard, outer shell on the surface, which is formed by collision among the moving particles and collision of the moving particles with the side walls of the granulator, while the particle core is less dense.
If the percentage of heat shrinkage between the core portion and the surface layer of a particle differs, the surface layers may peel, so breaking the particles, during or after calcination of the particles. If strips of extrusion-shaped particles are granulated by a rotary granulator, the above mentioned problem of the outer surfaces of the particles becoming dense is alleviated, but it is not solved entirely.
In Japanese Patent Laid-Open No.1998-17321, a method for obtaining small spheres by rotary granulation was disclosed, and it is mentioned that a high strength can be achieved. However, this method is used to produce a porous material with many small pores of 100 xc3x85 (10xe2x88x9210 meters) or less in diameter, and while it is effective for producing a gas adsorbent or a hydrotreating catalyst for a low-molecular oil, it is not yet satisfactory for producing a hydroprocessing catalyst for a heavy oil requiring many large pores. Besides, there is also the problem that if it is attempted to granulate a sticky compound, the raw material is liable to form lumps by mutual cohesion. Since an inorganic hydrous cake or paste mainly containing alumina is relatively highly sticky, it is necessary to further improve the conventional rotary granulation methods.
On the other hand, Japanese Patent Publication No. 1989-37332, Japanese Patent Laid-Open No. 1990-51418, and Japanese Patent Publication No.1995-24749 disclose the so-called oil-drop method for preparing spherical oxide particles. In these methods a mineral acid or organic acid is added to an alumina powder to form a partial sol dispersion and this is added to an oil layer in the form of droplets, for gelation. These methods have solved the problem caused by the rotary granulation methods in that the particles produced by way of the oil drop method are internally homogeneous. However, it is very costly to manufacture the equipment for these techniques, and it is difficult to control the pore structure as desired. Moreover, to make the size of the obtained particles uniform, a high level of technical skill is required for maintaining proper droplet-forming conditions, solidification conditions, etc. Besides, even the products obtained by these methods of solidification in oil cannot satisfy all of form, breakage strength, and abrasion resistance.
Thus, there is need for a process for producing spherical oxide particles with a uniform particle size and a homogeneous density, that is, where there is substantially no difference in density between the core portions of the oxide particles and the surface portions. This is to ensure that the spherical particles are high in abrasion resistance. The process should be suitable for producing particles of various sizes, in particular with a diameter between 0.5 and 7 mm, preferably with a diameter between 2 and 7 mm. The process should be easy to regulate, and be capable of producing particles with a large pore size and a narrow average particle size distribution.
To solve the above need, the inventors, in one embodiment of the invention, developed a process for preparing spherical oxide particles which comprises the steps of shaping a starting material comprising an oxide hydrate into particles of substantially constant length by leading it to a set of two rolls rotating towards each other, followed by leading the material to a roll equipped with grooves to form rod-type shapes, cutting the rod-type shapes into particles of substantially constant length, converting the thus formed particles into spheres, and heating the particles to convert the oxide hydrate into an oxide.
A second embodiment of the invention comprises spherical oxide particles having a wear rate of less than 0.5 wt %, more preferably less than 0.1 wt % and substantially no difference in density between the core portion of the particles and the surface portion of the particles.
In a third embodiment of the invention, the inventors developed A process for preparing a hydroprocessing catalyst in which a Group VI and/or a Group VIII metal component are incorporated into spherical oxide particles prepared by way of a process comprising the steps of shaping a starting material comprising an oxide hydrate into particles of substantially constant length by leading the material to a set of two rolls rotating towards each other followed by leading the material to a roll equipped with grooves to form rod-type shapes, cutting the rod-type shapes into particles of substantially constant length, converting the thus formed particles into spheres, and heating the particles to convert the oxide hydrate into an oxide.
Other embodiments of the invention encompass details about the making of the spheres, the properties of the spherical oxide particles, metal components of the hydroprocessing catalyst and the use of the catalyst in a process for the hydroprocessing of a hydrocarbon feed, etc., all of which are hereinafter disclosed in the following discussion of each of the facets of the present invention.